Download Electricity Industry EMF Measurement Protocol for High Field Area

ENERGY NETWORKS ASSOCIATION
Electricity Industry EMF Measurement Protocol for High Field Areas
Contents
1
2
3
4
5
Introduction
1.1
Background
1.2
High Field Areas
High Field Area - Generation Businesses
2.1
Thermal generation
2.2
Hydro-electric generation
High Field Area - Transmission Businesses
High Field Area – Distribution Businesses
Measurement Procedure
Appendix 1: Example of Measurement Approach for Major Plant Items.
Appendix 2: Details of Typical Meters.
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Introduction
1.1
Background
This protocol was prepared by the esaa EMF Advisory Committee in June 2004. When the
responsibility for the EMF issue was transferred to the Energy Networks Association (ENA) in
2006, this protocol was also transferred. The protocol is reviewed periodically to ensure
relevance and is currently in use within the industry.
The protocol will assist businesses in the electricity supply industry to:
 identify possible areas of high electric and magnetic fields (EMF) associated with their
business operations; and
 measure high electric and magnetic fields in these work areas or locations.
Measurements made can then be used to assess compliance with present, recommended EMF
exposure limits and any future EMF standard that may be adopted. This will result in improved
protection of the health and safety of employees and the public.
The current limits of EMF exposure applicable to Australia are those in the National Health and
Medical Research Council (NHMRC) Radiation Health Series publication No. 30 "Interim
guidelines on limits of exposure to 50/60Hz electric and magnetic Fields (1989)" which is
available from the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA)
website (www.arpansa.gov.au). These limits of exposure are generally not regulated or
enforceable but constitute good practice and are generally followed by the electricity supply
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industry. However, they are called up by regulations in some jurisdictions, e.g. Victoria, where
compliance is required.
A more recent exposure standard by the International Commission on Non-Ionising Radiation
Protection (ICNIRP) of 1998 has been adopted for use in some overseas countries, particularly
those of the European Union. In 2002, the Institute of Electrical and Electronics Engineers
(IEEE) of the USA produced their first EMF (0 to 3 kHz) standard C95.6. It uses a different
approach to the ICNIRP standard in deriving exposure limits and it is available from the IEEE. It
has not yet been adopted in any country as a national standard.
This protocol covers generation (thermal and hydro) and network (transmission and distribution)
businesses’ areas of possible high electric and magnetic fields and considers employee and
public exposures.
For the protocol, magnetic flux density is described in units of milligauss (mG rms) and
electric field strength is in units of kV/metre (rms). (Note that 1mG equals 0.1 microtesla in SI
units.) It should be noted that magnetic flux density is dependent on the current flowing and
varies continuously as the load varies on any piece of electrical apparatus. However the electric
field, being voltage dependent, is relatively stable over time.
Note that EMF measurements in residences are described in the ENA “Protocol for
Measurement of Residential Electric and Magnetic Fields” available on the ENA web site
www.ena.asn.au/emf.
1.2
High Field Areas
For this document, high field areas are considered to be those that may be comparable to or
exceed the NHMRC or ICNIRP recommended limits of exposure at power frequencies in Tables
1 and 2.
Table 1. NHMRC (1989) recommended EMF limits of exposure
Electric Field
Magnetic Flux
Strength (kV/m)
Density (mG)
Occupational
10
5000
 Whole working day
30
50000
 Short term
250000
 For limbs
General Public
 Up to 24h/day
 Few hours/day
5
10
1000
10000
Table 2. ICNIRP (1998) recommended EMF limits of exposure
Electric Field
Magnetic Flux
Strength (kV/m)
Density (mG)
Occupational
5000
10
 Whole working day
General Public
 Up to 24h/day
5
1000
Note: short-term or instantaneous values.
2
Table 3 shows the corresponding limits of exposure for the IEEE standard for comparison.
Table 3. IEEE (2002) recommended EMF limits of exposure
Electric Field
Magnetic Flux
Strength (kV/m)
Density (mG)
Occupational
20
27100
 Whole working day
758000
 For limbs
General Public
 Up to 24h/day
 Extremities
5*
-
9040
758000
* Except 10 in power line right of way (easement)
Occupational limits of exposure apply to employees and contractors of the business who, by
their training or experience, would be aware of possible risks associated with EMF from various
sources.
General public limits of exposure apply to all others, such as employees of the business,
visitors, etc., who from their backgrounds would be unaware of possible risks associated with
EMF from various sources.
The protocol provides guidance on
 high field areas of possible interest;
 suggested measurement procedures; and
 some samples of measurement approaches.
2 High Fields Areas - Generation Businesses
For generating businesses, high magnetic flux density areas are more common than high
electric field strength areas. When considering areas to be assessed in an EMF survey,
exposure areas related to employees and the public should be considered separately.
Normally, the public would only have close access to plant items in association with business
staff or tour guides.
2.1
Thermal generation
Magnetic flux density assessment
As magnetic flux density is related to the current flowing in conductors, areas and items of plant
that have large current flows (above 250A) should be considered. As a guide, areas within 10
metres of the current flow should be considered. Previously identified areas and items of plant
are:
a)
Busbars between the generator, step up transformers and auxiliaries transformers
The output of large generators can be several thousand amperes and thus high magnetic fields
are common. Many power stations use phase isolated busbars (PIB) to connect the generator
to step up transformers (see Figure 1). Areas around the PIB should be assessed for high
magnetic fields including walkways, between the individual busbars, access ladders over the
PIB and PIB connections to the step up and auxiliary transformers.
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It is noted that access is sometimes permitted to the top of step up and auxiliary transformers
and thus magnetic field assessment should be considered for these locations.
The generator star point and, if applicable, the main generator circuit breaker should be also
assessed.
Magnetic field measurements should be carried out when the generator is at maximum load and
at full reactive capability to ensure that full load currents are flowing through the busbars. For
generators of several thousand ampere output, magnetic fields over 5000mG may be expected.
Figure 1. Busbars between a generator, step up transformers and auxiliaries
transformers
b)
Cabling between large transformers and switchboards:
As the cabling between large transformers (secondary side) and switchboards can carry large
currents, the route of the connecting cable should be assessed (see Figure 2). Areas include:
 secondary side terminal boxes of the transformers;
 cable tunnels/trays accessible by staff; and
 switchboard's incoming cable cubicles.
Magnetic field measurements should be carried out when the transformer/switchboard is fully
loaded.
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Figure 2. Secondary side of large transformer should be assessed
c)
Cabling between switchboards and large motors or loads
As the cabling between switchboards and large motors or loads can carry large currents, the
route of the connecting cable should be assessed. Areas include:
 area surrounding switchboard circuit breaker;
 cable tunnels/trays accessible by staff; and
 motor (or load's) terminal box (see Figure 3).
Magnetic field measurements should be carried out when the motor (or load) is at full current
capacity.
d)
Miscellaneous areas
Other areas to be considered are:
 around the generator's operating and mezzanine floor area;
 guided tour routes;
 cable pits, trenches and tunnels; and
 control room, workshops, office areas and often used access ways (e.g. tunnels) that
may be in close proximity to large current flows.
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Figure 3. Cabling between switchboard and large motor.
Electric Field Strength assessment:
As noted above, there are fewer areas of high electric field strength in the generating
businesses.
As electric field strength is related to the operating voltage of the equipment and the separation
between source and measuring point, areas and items of plant that have high voltages and
close approach distances should be considered. Screening can effectively mitigate high electric
fields and the vast majority of equipment in the generating facility is well screened. As a guide,
areas with no screening, high voltages (3.3kV or above) and short approach distances (a few
metres or less) should be considered. The only previously identified area of high electric field
strength in generating businesses is in areas which have overhead lines such as the generator
(step-up) transformer and switchyard areas (see Figure 4). These areas are covered in more
detail in section 3.
2.2
Hydro-electric generation
The high field areas for a hydro-electric generation business will be similar to the comparable
areas in a thermal generation business.
Special consideration should be given to underground areas, such as cable pits, trenches and
tunnels, with high voltage cables installed. These may cause employees or the general public
to be in close proximity to cables carrying heavy currents and thus may result in high magnetic
or electric fields.
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Figure 4. Overhead lines in a generator (step-up) transformer and switchyard area.
3
High Field Areas - Transmission Businesses
Magnetic field is the primary issue, but electric field should also be recorded particularly in areas
where persons may come into relatively close proximity to high voltage facilities - such as
busbars in the case of substations and low conductors (normally mid span) of transmission
lines.
When considering areas to be included in the survey, exposures in two categories, occupational
and the general public, need to be considered separately.
 Occupational exposure assessment includes areas visited by workers (employees and
contractors) for maintenance, inspections, etc., and may require personal monitoring for
those carrying out tasks in high field environments.
 General public exposure assessment includes areas accessible to the general public.
This would not normally include substations, which are a controlled environment and are
only accessible to authorised persons or visitors under supervision of staff. It may apply
to exposure in areas associated with transmission lines.
The following is not an exhaustive list, but offers guidance and suggestions.
Occupational Exposure - Substations
Examples of areas to be surveyed (limited duration occupancy) are:
 busbars;
 HV cables;
 around switchgear including operating or inspection positions;
 transformer bays - around cables and switchgear, etc.;
 cable pits, trenches and tunnels;
 under and adjacent to HV landing span; and
 high current equipment, such as static var compensators (SVC).
Examples of areas to be tested (extended duration occupancy) are:
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




switchboards;
electrical switchgear rooms;
control rooms;
workshops; and
offices and workstations.
Figure 5. Transformer bay in transmission substation
Note that when live substation maintenance techniques are in use, some workers will be in high
field environments (see comments below for lines)
Occupational Exposure - Lines
Live-line work requires an assessment of work methods and procedures to identify the tasks
and areas of closest proximity to the energised conductors.
General Public Exposure - Substations
Normally the public do not have access to transmission substations; access would be limited to
areas immediately outside the security fence. Such areas close to major plants items or low
lines may need to be assessed.
General Public Exposure - Lines
Magnetic field levels in the vicinity of overhead transmission lines are unlikely to be close to current
guideline limits; a desktop review of selected spans may be useful to confirm this. Magnetic field
levels in the vicinity of underground transmission lines should be reviewed to ensure that fields at
ground level do not approach current guideline limits.
Electric fields may, however, be quite substantial (5kV/m or greater) in some areas where the pubic
has access, particularly under spans of 330 and 500kV transmission lines. Line profiles, mapping
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and aerial photography may be used to identify these spans. Underground cables will not produce
electric fields at the surface.
4
High Field Areas - Distribution Businesses
Magnetic fields are the primary issue, but electric fields should also be recorded, particularly in
areas where persons may come into relatively close proximity to medium voltage facilities - such
as busbars in the case of substations and low conductors (normally midspan) of distribution
and/or sub transmission lines.
When considering areas to be included in the survey, exposures in two categories, occupational
and the general public, need to be considered separately.
 Occupational exposure assessment includes areas visited by workers (employees and
contractors) for maintenance, inspections, etc., and may require personal monitoring for
those carrying out tasks in high field environments.
 General public exposure assessment includes areas accessible to the general public.
This would not normally include substations, which are a controlled environment and are
only accessible to authorised persons or visitors under supervision of staff. It may
include areas immediately adjacent to distribution substations, especially areas near low
voltage switchboards and/or cabling.
The following is not an exhaustive list, but offers guidance and suggestions
Occupational Exposure - Substations
Examples of areas to be surveyed (limited duration occupancy) are:
 busbars;
 HV cables;
 around switchgear including operating or inspection positions;
 cable pits, trenches and tunnels;
 transformer bays - around cables and switchgear, etc.; and
 under and adjacent to HV landing span.
Examples of areas to be tested (extended duration occupancy) are:
 switchboards;
 electrical switchgear rooms;
 control rooms;
 workshops; and
 offices and workstations.
Note that with the introduction of live substation maintenance techniques, some workers will be
in high field environments (see comments below for lines).
Occupational Exposure - Lines
Live-line work requires an assessment of work methods and procedures to identify the tasks
and areas of closest proximity to the energised conductors.
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General Public Exposure - Substations
Normally the public does not have access to zone substations, and access would be limited to
areas immediately outside the security fence or building. Such areas close to major plants
items or low lines may need to be assessed.
For substations in CBD areas and high-rise buildings in particular, areas immediately adjacent
to distribution substations, especially areas near low voltage switchboards and/or cabling may
need to be assessed.
General Public Exposure - Lines
Magnetic field levels in the vicinity of distribution and sub-transmission lines, whether these are
overhead or underground, are unlikely to be close to guideline limits.
Electric fields could be recorded, particularly in areas where persons may come into relatively
close proximity to medium voltage facilities such as low conductors (normally midspan) of
distribution and/or sub transmission lines.
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Measurement Protocol
If measurements are to be taken of high field areas, it is recommended that
 a clear purpose and scope of the measurement program be prepared; and
 suitably trained and experienced personnel are used.
The measurements and their documentation should be undertaken in the following manner:
a) Use a suitable measurement standard (for example as the ANSI/IEEE standard 6441987 "IEEE Standard procedures for measurement of Power Frequency Electric and
Magnetic Fields from AC Power Lines").
b) Use of suitable measurement equipment such as the EMDEX II RMS power frequency
magnetic field exposure meter and an AC RMS Electric Field Meter (such as Monroe
Electronics Inc). See examples in Appendix 2.
c) Set equipment at maximum current and normal voltage levels.
d) Take spot measurements to ascertain existence of high field areas.
e) Measurements should be representative of normal working conditions and thus should
be taken at 0m, 1m and 2m heights for a standing person. If above ground access is
possible then measurements should reflect possible access locations. The
measurements do not represent whole body exposures.
f) For magnetic fields, measurements should be in a 1m grid around the equipment or in
the area where a person may need to be located to operate or inspect a particular piece
of apparatus.
g) The following information should be documented:
 measurement method used;
 instruments used including calibration detail;
 persons undertaking the measurement;
 heights that measurements were taken;
 diagram of measurement grid and equipment outline;
 units of measurement;
 date and time of measurement;
 current flowing in equipment;
 voltage level in equipment; and
 results and report conclusions.
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Appendix 1: Example of Measurement Approach for Major Plant Items:
Example 1: Magnetic Field measurement around a generating business's major auxiliary
transformers
The following picture shows a major auxiliary transformer (22kV/11kV 38MVA). The survey
concentrates on the phase isolated bus connection on top of the transformer (which is
accessible to maintenance staff via ladder) and the secondary side terminal box. It is noted that
the magnetic fields inside the transformer are concentrated and contained in the transformer's
core laminations and thus are generally not a source of high fields. The measurements would
be taken at ground level, 1m, 2m and 3m off the ground to cover the area that could be
accessed during normal operations and maintenance.
Figure A1. Cabling between large transformer and switchboards
Measurements taken at:
Ground Level
1 metre
2 metre
3 metre
X
X
X
Transformer
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Cable Terminal
Box
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Date:
Time:
Measurement person:
Transformer load (MVA) =
Transformer voltage (Primary) =
Measurements in mG
Scale:
0.5 metre
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X
Appendix 2: Details of Typical Meters
ELECTRIC FIELD METER:
Manufacturer:
Monroe Electronics Inc. Lyndonville Kentucky USA
Model: 238A – 1
Technical Specifications:
Analogue Scale readout – full scale options 5, 10, 25 kV / m – minimum reading is effectively
0.05 kV / m
Other details are not available
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EMDEX II High Field Magnetic Field Meter
Manufacturer:
Enertech Consultants, 300 Orchard City Drive 17 Main Street Suite #132 P.O. Box 770
Campbell, CA 95008
Technical Specifications
Data Collection Actual Measurements
Range 0.004 - 120 G (0.4 µT - 12 mT)
Resolution 4 mG (0.4 µT)
Typical Accuracy ± 1%
Frequency Broadband: 40 - 3,000 Hz; Harmonic: 100 - 3,000 Hz
Max Sample Rate 1.5 Seconds
Internal Memory 156 Kb or 512 Kb
Display (mG or mT units) Alphanumeric 8-Character
Measurement Method True RMS
Typical Battery Life Alkaline: Up to 7 Days; Lithium: Up to 21 Days
Dimensions 6.6" x 2.6" x 1.5" (16.8 x 6.6 x 3.8 cm)
Weight 12 ounces (341 grams)
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HMI Systems EMF Survey Meter
Manufacturer:
HMI Systems, 32 Grant Street, East Malvern, VICTORIA 3145
Technical Specifications
Digital Magnetic Field Survey Meter
Meter Purpose
Range
0.1 – 6 000 mG (0.01-600 µT)
Resolution
0.1 mG (0 – 99.9 mG), 1 mG (>100 mG),
Typical Accuracy
± 2%
Frequency Response
Sample Rate
30 - 1,000 Hz
1.0 seconds
Measurement Method
True RMS in three axes and resultant
Typical Battery Life Alkaline: Over 48 Hours
Dimensions
120 x 60 x 25 mm
Weight
95 g (without battery)
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